It is well known in the petroleum industry that some hydrocarbon-bearing formations are weakly consolidated or, in fact, may be unconsolidated formations. While such formations are known to contain substantial quantities of oil and gas, the production of oil and gas from these formations is difficult because of the movement of particulates such as sand particles and other finely divided particulate solids from the unconsolidated or weakly consolidated formation into the wellbore. This movement is a result of the movement of fluids and may be a result of the differential pressure between the formation and the wellbore created by pumping or by the production of fluids upwardly through the wellbore. Some formations are weakly consolidated or unconsolidated initially and others become weakly consolidated as a result of the production of fluids from the formation, especially when water is present in the produced fluid. Formations of this type are formations which are, at least in part, consolidated by the presence of clays in the formation. Such clays can become dispersed and expanded by the production of aqueous fluids from the formation, thereby weakening the overall formation to the point where it becomes unconsolidated or weakly consolidated with the resulting production of particulates into the wellbore. As a result, uncemented, weakly consolidated or unconsolidated formations impose limits on the draw-down pressure which can be used to produce fluids from the formation. This limits the rate at which fluids can be produced from the subterranean formation.
One approach used to prevent the movement of particulates into the wellbore is the use of gravel packs. Gravel packs comprise a gravel sheath positioned around the inside of a casing, slotted liner, perforated casing or the like, or the wellbore in an open hole through the producing formation to limit the production of particulate materials from the weakly consolidated or unconsolidated subterranean formation. Gravel packs can be effective when the gravel pack sand is approximately six times the size of formation sand.
The positioning of gravel packs is expensive and requires that the well be shut down for a period of time while a work-over rig is placed over the well to pull and run the tubing. The formation may also be damaged by the operations necessary to place the gravel pack. As a result, it is relatively expensive to position gravel packs in wells to prevent the flow of particulate matter from unconsolidated or weakly consolidated formations into the wellbore.
Accordingly, improved methods have been sought for strengthening subterranean formations to inhibit the production of sand and other finely divided particulate material into the wellbore while still maintaining the ability of the formation to produce fluids into the wellbore.